1. Field of the Invention
The present invention is directed to heating resistors comprising a conducting oxide and a nonconducting oxide and liquid ejecting heads and other devices comprising the heating resistors.
2. Background Art
FIG. 1 provides a schematic representation of the process of liquid ejection from a conventional representative liquid ejecting head. The process of liquid ejecting included the following steps: i) a heating resistor is heated by applying an electric signal to the exterior of the heating resistor, thereby temporarily heating an adjoining printing liquid above a boiling point of the liquid to form bubble cores; ii) the bubble cores grow or coalesce to form a super bubble, and as a result the printing liquid fills the chamber of the liquid ejecting head and becomes pressurized; iii) the printing liquid in the vicinity of a nozzle or outlet is dispensed to the outside of the chamber in the shape of a droplet, and the supper bubble collapses; and iv) the printing chamber is recharged with additional printing liquid via a capillary vessel. During the ink-dispensing process collapse of the super bubbles causes a strong pressure to be locally applied to the surface of the heating resistor, the pressure being called a cavitation force. The cavitation force can create defects in the heating resistor and may be a reason for a reduced lifetime observed in many printing devices that operate by this process of liquid ejection (see, e.g., Aden, J. S. et al., “The Third-Generation HP Thermal InkJet Printhead,” Hewlett-Packard Journal 45:41-45 (1994) and Lim, J. et al., “Failure mechanisms in thermal inkjet printhead analyzed by experiments and numerical simulation,” Microelectronics Reliability 45:473-478 (2005)).
FIG. 2 provides a schematic cross-sectional view of the major parts of a conventional substrate used in a liquid ejecting head. Referring to FIG. 2, the conventional liquid ejecting typically comprises a silicon substrate (201) having deposited thereon a plurality of layers that provide a driving circuit and a heating resistor. The heating resistor (203) heats a printing liquid when an electrical signal is applied to the heating resistor by an electrode (204). Typically, an insulating layer (202) is formed between the silicon substrate (201) and heating resistor (203) to provide thermal and electric insulation between the heating resistor (203) and the silicon substrate (201). A patterned electrode layer (204) is formed adjacent to the heating resistor (203) and applies an electric signal to the heating resistor. The electrode layer typically comprises a metal conductor. Protection layers (205, 206) are formed on the surface of the electrode (204) and heating resistor (203) to protect the electronically active elements from chemical and/or mechanical damage associated with thermal cycling of the heating resistor (203) and also to electrically insulate the heating resistor (203) and electrode layer (204) from the printing liquid.
In general, the heating resistor should have the following properties:                (1) a controlled electrical resistivity within a proper scope to be applied to liquid ejecting systems;        (2) a low temperature coefficient of resistance (TCR) so that the change of the electrical resistance in accordance with a temperature is minimized; and        (3) chemical, mechanical and electrical stability during thermal cycling.        
Materials for use in heating resistors for liquid ejecting head that have been conventionally used include: HfB2 (U.S. Pat. Nos. 6,375,312 and 6,013,160), TaAl (U.S. Pat. Nos. 3,852,563, 4,513,298 and 4,965,611), poly-Si (U.S. Pat. No. 4,532,530), Ti/TiNx (U.S. Pat. No. 5,870,121), α-Ta (U.S. Pat. No. 6,395,148), TaN0.8 (Korean patent laid-open publication 10-1994-0014946 and U.S. Pat. Nos. 6,375,312 and 6,382,775), and TaSiN (U.S. Pat. No. 6,527,813). However, these materials can exhibit degradation during thermal cycling. Moreover, no other materials complying with the above requirements except the conventional materials have been reported. Therefore, what is needed are new materials for use in thermal resistor elements and ink ejecting devices that integrate these new materials to enable the manufacture of printing devices having longer lifetimes and greater reliability.